The present invention relates to a blade/vane cascade segment, a blade/vane cascade, a stage and a blade/vane channel of a turbomachine, as well as a turbomachine.
Turbomachines (such as gas and steam turbines) generally have a flow channel for conducting a fluid. The flow channel, which is also called an “annular space” is bounded radially inside by the shaft of a rotor and radially outside by a housing; the designations “radially” as well as “axially” and “peripheral direction”, and terms derived therefrom in this document are always understood to be with reference to an axis of rotation of the rotor—as long as nothing is indicated to the contrary.
Blade/vane cascades (for which the name “blade/vane ring” is also common) are arranged in the annular space of a turbomachine. They each comprise guide vanes or rotating blades that lie one behind the other in the peripheral direction at essentially regular distances, as well as stages belonging thereto, which are also called “cover plates”, and that have a stage edge on the inflow side and a stage edge on the outflow side. These stage edges bound the stage surface facing the blades/vanes (or blade/vane elements) in the axial direction.
In this document, the stage edge “on the inflow side” is designated as the edge of the stage, by which the leading (axial) principal flow first passes into the annular space of the turbomachine during operation; correspondingly, the stage edge “on the outflow side” is the other edge. The indications “downstream” or “upstream”, respectively, refer correspondingly to the axial principal flow direction, and thus only to the axial position, regardless of a possible displacement in the peripheral direction: In this document, in particular, a point given as lying “downstream of the inflow edges” (or downstream of another point) is to be understood if the point is arranged offset axially in/with the principal flow direction (thus following it), in comparison to a direct connection of the inflow edges to the surface of the stage (or in comparison to another point); this is valid analogously for the designation “upstream” (with the opposite direction).
The distance of the inflow edges of the blade/vane elements from their outflow edges, which is measured in the direction of the provided axial principal flow is named the “cascade width”.
The pressure side of a blade/vane and the suction side of an adjacent blade/vane each bound a so-called blade/vane channel in the peripheral direction. In the radial direction, this blade/vane channel is bounded by so-called side walls within the turbomachine. These side walls are formed, on the one hand, by the stages, and, on the other hand, by sections lying radially opposite to these stages: In the case of rotating blades, such a side wall in this case is a section that lies radially outside (in particular, a section of the housing); in the case of guide vanes, it is a radially inner-lying section (in particular, a rotor hub).
A fluid flow guided through a flow channel is periodically influenced by the surfaces of the side walls. Flow layers that run next to these surfaces are more strongly diverted here, due to their slower speed, than flow layers that are further away from the side walls. Thus, a secondary flow that is superimposed on an axial principal flow arises and, in particular, leads to vortexes and pressure losses.
In order to reduce secondary flows, contouring is frequently introduced in the side walls in the form of elevations and/or depressions
A plurality of these types of so-called “side wall contouring” is known from the prior art.
By way of example, the patents or patent applications of the Applicant will be named: EP 2 487 329 B1; EP 2 787 172 A2; and EP 2 696 029 B1. The last-named publication discloses therein a blade/vane cascade with a side wall contouring that has a pressure-side elevation and a suction-side depression, wherein a highest section of the elevation and a lowest section of the depression lie in a region from 30% to 60% of the extension of the blade/vane elements in the axial direction and differ from one another by a maximum 10% in the axial direction.
The publication US 2012/051 900 A1 discloses a guide vane cascade with a side wall contouring, in which a stage surface has an elevation and a depression between the pressure side of one of the vane elements and the suction side of another of the vane elements, and together these form an axially extending arcuate channel.
A blade/vane cascade with a stage is known from US 2006/233 641 A1, the surface of which has elevations increasing in height from the inflow and outflow edges of the blade/vane elements.